Group III nitride semiconductor, for example, a gallium nitride (GaN) based semiconductor is expected to be used as a material for next-generation semiconductor devices. The GaN based semiconductor device includes a wider bandgap than that of a silicon (Si) semiconductor device, and thus can achieve a high breakdown voltage and a low loss in comparison to the Si semiconductor device.
A High Electron Mobility Transistor (HEMT) structure using a two-dimensional electron gas (2DEG) as the carrier is widely applied to a field effect transistor using a GaN based semiconductor. Unfortunately, a phenomenon called current collapse occurs in a field effect transistor having such an HEMT structure.
The current collapse is a phenomenon that the application of high drain voltage to a field effect transistor results in increase of on-resistance. To predict the influence of the current collapse on a circuit configured to operate at a high frequency, it is preferable to evaluate the current collapse occurring just after the switching of the field effect transistor.